Image pickup system

ABSTRACT

The invention relates to an image pickup system comprising an electronic view finder suitable for achieving compactness and having a sufficient viewing angle of field and satisfactory optical performance. The image pickup system comprises an image pickup device, an image display device for displaying an image, a controller for converting image formation obtained from the image pickup device into a signal that enables the image information to be formed on the image display device, and a viewing optical system for guiding an image displayed on the display device to a viewer&#39;s eye. The viewing optical system comprises at least three lenses.

This application claims the benefit of Japanese Application No.2001-21491 filed in Japan on Jan. 30, 2001, the contents of which areincorporated by this reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to an image pickup system suchas a silver-salt or digital camera, and more particularly to an imagepickup system comprising an electronic view finder suitable for use witha compact image display device, especially a reflection type liquidcrystal display device.

Most of silver-salt or digital cameras comprise means for recordingimages picked up by an image pickup optical system and a viewing opticalsystem for checking an image pickup range. For the recording of images,chemistries on film surfaces are used in the case of silver-saltcameras, and information obtained through photoelectric conversion atelectronic image pickup devices such as CCDs are employed in the case ofdigital cameras.

On the other hand, most of viewing optical systems are of the typedesigned to form an image on the retina of a viewer's eye, therebyviewing the image to be picked up. This type of viewing optical systemdoes or does not comprise an image pickup optical system for forming animage to record a part of the entrance side. A typical example of theformer is a single-lens reflex camera, and that of the latter is a realimage type finder suitable for use on a zoom optical system, includingan objective optical system, an image-erecting means and an eyepieceoptical system and now mounted on most products. These are oftencollectively called an optical finder.

In many cases, digital cameras or video cameras are put on the marketwhile they are provided thereon with an electronic finder designed todisplay an image on an LCD (liquid crystal display device) rather thanan optical finder, so that the image pickup range can be checked byallowing an observer to have a direct view of the image. Digital cameraswith both an optical finder and an electronic finder mounted thereon,too, are now commercialized.

Furthermore, the so-called EVF (electronic view finder) designed to viewimages on LCDs via a viewing optical system is proposed. Forconventional commodities with such an electronic finder mounted thereon,there is used a display device with a display screen having a diagonallength of about 0.5 inches or 12 mm.

However, there are growing demands for size reductions of cameras. Theassociated viewing optical system has been designed in conformity withconventional LCD size; the whole size of the viewing optical systemcannot be reduced or some limitations are placed on further sizereductions of image pickup systems.

Meanwhile, some LCDs have been developed with size smaller than so farachieved. However, when such LCDs are used with an electronic viewfinder, existing viewing optical systems offer a problem that the angleof field for viewing subjects becomes small depending on LCD size sothat satisfactory observation becomes difficult.

Further, as the whole size of a viewing optical system is reduced inconformity with LCD size, some inconveniences such as failures inobtaining the eye relief necessary for observation are unavoidable.

Furthermore, as the magnification of the viewing optical systemincreases with decreasing image display device size, not only ischromatic aberration of magnification likely to occur but there is alsoa problem that dust, etc. deposited on the viewing optical system isvisible on an enlarged scale.

To add to this, when a reflection type display device with light raysincident on its display screen side is used as the image display device,it is required to get hold of the separate optical path necessary fordisplay purposes.

SUMMARY OF THE INVENTION

In view of such problems as mentioned in conjunction with the prior art,the present invention has been accomplished to achieve any one of thefollowing objects.

One object of the invention is to provide an image pickup system with anelectronic view finder mounted thereon, which is suitable for achievingcompactness.

Another object of the invention is to provide an image pickup systemthat allows viewers to have an easy grasp of an image pickup range.

Yet another object of the invention is to provide an image pickup systemthat ensures a sufficient viewing angle of field and satisfactoryoptical performance even when used with an image display device having ashort diagonal length of its display surface.

Still yet another object of the invention is to provide an image pickupsystem having an electronic view finder well corrected for chromaticaberration of magnification.

A further object of the invention is to provide an image pickup systemhaving an electronic view finder, where dust, etc., if deposited on aviewing optical system, are virtually unnoticeable,

A further object of the invention is to provide an image pickup systemwith an electronic view finder mounted thereon, which enables opticalelements to be appropriately located even when a reflection type imagedisplay device is used as an image display device.

A further object of the invention is to provide an image pickup systemhaving an electronic view finder capable of accomplishing a plurality ofsuch objects as mentioned above.

According to the first aspect of the invention, there is provided animage pickup system comprising an image pickup device, an image displaydevice for displaying an image, a controller for converting imageformation obtained from said image pickup device into a signal thatenables said image information to be formed on said image displaydevice, and a viewing optical system for guiding an image displayed onsaid display device to a viewer's eye, characterized in that:

said viewing optical system comprises at least three lens elements, atleast two of which are cemented together to form a doublet component.

An account is now given of what is achieved by the first image pickupsystem.

To achieve the necessary angle of field (of, e.g., 22°) at the diagonallength of the display screen of an image display device in aconventional image pickup system, an eyepiece magnification of around 7would be plenty good enough. However, to obtain a sufficient angle offield in the case where a smaller image pickup device is used, too, itis required for a viewing optical system to have a higher eyepiecemagnification than a conventional one. To ensure a sufficient angle offield and satisfactory optical performance even when such a smallerimage display device is used, therefore, it is required to use at leastthree lenses for the viewing optical system. This then enables thenumber of refracting surfaces to be so increased that any sharprefraction by refracting surfaces can be prevented, resulting in asensible tradeoff between correction of aberrations and ensuring thenecessary angle of field.

A lens arrangement consisting of two positive lenses and one negativelens or three lenses in all is more preferable in consideration of cost,because chromatic aberrations and other aberrations can be correctedwith a reduced number of lenses.

The doublet component is not only effective for correction of chromaticaberrations but can also have a larger thickness as compared with a lensarrangement comprising separate single lenses. It is thus possible toreduce lens tilt errors on assembly. It is here noted that when theimage pickup optical system used is of an interchangeable type, thepresent invention also includes an image pickup system proper alone.

According to the second aspect of the invention, the image pickup systemof the first aspect is further characterized in that said viewingoptical system comprises two positive lens elements and one negativelens element.

What is achieved by the second image pickup system is now explained.

With the positive lenses and negative lens incorporated in the viewingoptical system, it is possible to make correction for a variety ofaberrations inclusive of chromatic aberration of magnification. With theuse of at least two positive lenses, positive power can be dispersedthroughout the viewing optical system so that spherical aberrationsliable to occur with increasing magnification can be well corrected.

According to the third aspect of the invention, the image pickup systemof the second aspect is further characterized in that one of said atleast two positive lens elements is cemented together with said onenegative lens element to form said doublet component.

What is achieved by the third image pickup system is now explained.

Chromatic aberration of magnification likely to occur when themagnification of the viewing optical system becomes high can be wellcorrected with the doublet.

According to the fourth aspect of the invention, the image pickup systemof the third aspect is further characterized in that at least one lenselement different from said doublet component in said viewing opticalsystem is a lens element having an aspheric surface.

What is achieved by the fourth image pickup system is now explained.

When an aspheric lens is used in a doublet, it is required to meet bothcementing precision and aspheric precision. However, if an asphericsurface is used for one single lens, it is then possible to improveyield with cost reductions. It is here noted that the action of positivepower becomes strong at the marginal region of the doublet. By using theaspheric surface at the surface spaced away form the doublet, it is thuspossible to make well-balanced correction for axial to off-axisaberrations occurring at the doublet.

According to the fifth aspect of the invention, the image pickup systemof the fourth aspect is further characterized in that said lens elementhaving an aspheric surface is a plastic lens element.

An account is now given of what is achieved by the fifth image pickupsystem.

By forming the lens with an aspheric surface using a plastic material,it is possible to improve processability.

According to the sixth aspect of the invention, the image pickup systemof the second aspect is further characterized in that at least one ofsaid two positive elements is a lens element having an aspheric surface.

What is achieved with the sixth image pickup system of the invention isnow explained.

It is preferable to use the aspheric surface in the positive lens,because cost reductions are achieved.

According to the seventh aspect of the invention, the image pickupsystem of the firth aspect is further characterized in that said viewingoptical system has an aspheric lens surface.

An account is now given of what is achieved by the seventh image pickupsystem of the invention.

As the magnification of the viewing optical system becomes high,off-axis aberrations are likely to occur. By the incorporation of anaspheric surface, however, it is possible to make well-balancedcorrection for axial to off-axis aberrations.

According to the eighth aspect of the invention, the image pickup systemof the first aspect is further characterized in that said viewingoptical system consists of two lens components or a doublet componentcomposed of one negative lens element and one positive lens element andone single-lens component whose absolute value for refracting power issmaller than either one of the absolute value for refracting power ofsaid positive lens element and the absolute value for refracting powerof said negative lens element.

According to the ninth aspect of the invention, the image pickup systemof the first aspect is further characterized in that said viewingoptical system comprises a single-lens element having an asphericsurface.

Reference is here made to what is achieved by the eighth and ninth imagepickup systems of the invention.

Main power for the viewing optical system is allocated to the doublet sothat aberrations from axial to off-axis ones are well balanced by thesingle lens. This single lens, because its optical power can be reduced,also makes it easy to form an aspheric surface thereon, so that areasonable tradeoff can be made between the number of lenses andcorrection of aberrations as well as processability.

According to the tenth aspect of the invention, the image pickup systemof the ninth aspect is further characterized in that said single-lenscomponent has positive refracting power.

Reference is now made to what is achieved by the tenth image pickupsystem of the invention.

By using the single lens in the form of a positive lens, it is furtherpossible to make satisfactory correction for spherical aberrations, etc.likely to occur at a viewing optical system of high magnification.

According to the eleventh aspect of the invention, there is provided animage pickup system of the first aspect, characterized in that saidviewing optical system consists of three lens elements or, in order fromsaid image display device side, a positive lens element, a negative lenselement and a positive lens element, while the first-mentioned positivelens element is cemented together with said negative lens element.

An account is now given of what is achieved by the 11th image pickupsystem.

Power is almost symmetrically allocated in +−+ order from the displaydevice side, so that a variety of aberrations inclusive of sphericalaberrations can be well corrected. A cemented surface for correction ofchromatic aberration of magnification can be defined by cementing thepositive lens on the display device side together with the negativelens.

Further, main power is allocated on the display device side by locatingthe doublet on the display device side, so that the display device islocated far away from the viewing optical system. This keeps diopterwith respect to dust, etc. deposited on the viewing optical systemremote from diopter with respect to the display screen, eliminating theinconvenience due to dust.

Furthermore, it is easy to save space for the provision of a reflectingsurface for guiding to the display screen the illumination light that isnecessary when a reflection type image display device is used as theimage display device.

According to the twelfth aspect of the invention, the image pickupsystem of the first aspect is further characterized in that said viewingoptical system consists of three lenses or, in order from said imagedisplay device side, a positive lens element, a positive lens elementand a negative lens element, while the second-mentioned positive lenselement and said negative lens element are cemented together.

What is achieved by the 12th image pickup system is now explained.

The principal point is shifted by allocating power in ++− order from thedisplay device side, so that the display device is located far away fromthe viewing optical system. This keeps diopter with respect to dust,etc. deposited on the viewing optical system remote from diopter withrespect to the display screen, eliminating the inconvenience due todust.

Further, a cemented surface for correction of chromatic aberration ofmagnification is defined by cementing together the positive lens on theviewer side and the negative lens.

Furthermore, it is easy to save space for the provision of a reflectingsurface for guiding to the display screen the illumination light that isnecessary when a reflection type image display device is used as theimage display device.

According to the thirteenth aspect of the invention, the image pickupsystem of any one of the 1st, 8th, 9th, 11th and 12th aspects is furthercharacterized by satisfying the following condition (1):1.0<b/a   (1)Here the small letter a is a distance from the display screen of theimage pickup device to the surface, nearest to the image display deviceside, of the viewing optical system, and the small letter b is a totallength from the surface, axially nearest to the image display deviceside, of the viewing optical system to the surface thereof nearest tothe viewer side.

What is achieved by the 13th aspect of the invention is now described.

Condition (1) is provided to balance the distance from the displayscreen to the viewing optical system with the total length of theviewing optical system. To obtain a large angle of field with a imagedisplay device of small size, it is required to keep the focal length ofthe viewing optical system short. However, as the lower limit of 1.0 tocondition (1) is not reached or the total length of the viewing opticalsystem becomes short, it is required to increase the angle of refractionof axial and off-axis light rays through the viewing optical system,resulting in spherical aberrations, coma, chromatic aberration ofmagnification, etc. being likely to occur. Otherwise., the distance fromthe display screen to the viewing optical system becomes too long toobtain the necessary angle of field. To reduce the whole size of theelectronic view finder, it is preferable to meet the following condition(1-1):1.0<b/a<3.5   (1-1)

The same as mentioned above goes true for the lower limit of 1.0 to thiscondition (1-1). As the upper limit of 3.5 is exceeded, it is difficultto achieve compactness even when a smaller image display device is used,because the total length of the viewing optical system becomes too long.Otherwise, the spacing between the display screen and the viewingoptical system becomes short; dust deposited on the viewing opticalsystem is more noticeable. In addition, it is difficult to take anoptical path for guiding illumination light when a reflection type imagedisplay device is used as the image display device.

More preferably, the following condition (1-2) should be satisfied:1.5<b/a<3.0   (1-2)

According to the fourteenth aspect of the invention, the image pickupsystem of any one of the 1st, 8th, 9th, 11th and 12th aspects is furthercharacterized by satisfying the following condition (2):1.0<a/c   (2)Here the small letter a is the distance from the display screen of theimage pickup device to the surface, nearest to the image display deviceside, of the viewing optical system, and the small letter c is a lengthof the short side of the display screen of the image display device.

What is achieved by the 14th image pickup system is now referred to.

Condition (2) is provided to define the length from the display screento the viewing optical system with respect to the length of the shortside of the display screen. As the lower limit of 1.0 to condition (2)is not reached, dust deposited on the viewing optical system is morenoticeable. In addition, when a reflection type image display device isused, it is impossible to take any reflection optical path for guidingillumination light thereto.

To reduce the whole size of the electronic view finder, it is preferableto meet the following condition (2-1):1.0<a/c<4.5   (2-1)

The same as set forth above holds for the lower limit of 1.0 to thiscondition (2-1). As the upper limit of 4.5 is exceeded, any compactnessis never achievable even with a smaller image display device, becausethe spacing between the image display device and the viewing opticalsystem becomes too large.

More preferably, the following condition should be satisfied:2.0<a/c<4.0   (2-2)

According to the fifteenth aspect of the invention, the image pickupsystem of any one of the 1st, 8th, 9th, 11th and 12th aspects is furthercharacterized by satisfying the following condition (3):1.4<f _(e) /a<2.4   (3)Here the small letter a is the distance from the display screen of theimage pickup device to the surface, nearest to the image display deviceside, of the viewing optical system, and f_(e) is a focal length of theviewing optical system.

What is achieved by the 15th image pickup system is now described.

Condition (3) is provided for the sufficient spacing between the displaydevice and the viewing optical system as well as for the necessary eyerelief. As the lower limit of 1.4 is not reached, it is difficult totake the eye relief necessary for observation. As the upper limit of 2.4is exceeded, on the other hand, it is difficult to take any angle offield plenty enough for observation.

More preferably, the following condition (3-1) should be met:1.6<f _(e) /a<2.5   (3-1)

According to the sixteenth aspect of the invention, there is provided animage pickup system comprising an image pickup device, an image displaydevice for displaying an image, a controller for converting imageformation obtained from said image pickup device into a signal thatenables said image information to be formed on said image displaydevice, and a viewing optical system for guiding an image displayed onsaid display device to a viewer's eye, characterized in that:

said viewing optical system comprises at least three lens elements, andthe following conditions (1) and (3) are satisfied:1.0<b/a   (1)1.4<f _(e) /a<2.4   (3)Here the small letter a is a distance from the display screen of theimage pickup device to the surface, nearest to the image display deviceside, of the viewing optical system, the small letter b is a totallength from the surface, axially nearest to the image display deviceside, of the viewing optical system to the surface thereof nearest tothe viewer side, and f_(e) is a focal length of the viewing opticalsystem.

Referring to what is achieved by the 16th image pickup system of theinvention, the actions obtained by meeting condition (1) for the 3rdimage pickup system and condition (3) for the 15th image pickup systemare attained in addition to those of the 1st image pickup system.

Thus, condition (1) is provided to balance the distance from the displayscreen to the viewing optical system with the total length of theviewing optical system. To obtain a large angle of field with a compactimage display device, it is required to keep the focal length of theviewing optical system short. However, as the lower limit of 1.0 tocondition (1) is not reached or the total length of the viewing opticalsystem becomes short, it is required to increase the angle of refractionof axial and off-axis light rays through the viewing optical system,resulting in spherical aberrations, coma, chromatic aberration ofmagnification, etc. being likely to occur. Otherwise, the distance fromthe display screen to the viewing optical system becomes too long toobtain the necessary angle of field. To reduce the whole size of theelectronic view finder, it is preferable to meet the following condition(1-1):1.0<b/a<3.5   (1-1)

The same as mentioned above goes true for the lower limit of 1.0 to thiscondition (1-1). As the upper limit of 3.5 is exceeded, it is difficultto achieve compactness even when a more compact image display device isused, because the total length of the viewing optical system becomes toolong. Otherwise, the spacing between the display screen and the viewingoptical system becomes short; dust deposited on the viewing opticalsystem is more noticeable. In addition, it is difficult to take anoptical path for guiding illumination light when a reflection type imagedisplay device is used as the image display device.

More preferably, the following condition (1-2) should be satisfied:1.5<b/a<3.0   (1-2)

Condition (3) is provided for the sufficient spacing between the displaydevice and the viewing optical system as well as for the necessary eyerelief. As the lower limit of 1.4 is not reached, it is difficult totake the eye relief necessary for observation. As the upper limit of 2.4is exceeded, on the other hand, it is difficult to take any angle offield plenty enough for observation.

More preferably, the following condition (3-1) should be met:1.6<f _(e) /a<2.5   (3-1)

According to the seventeenth aspect of the invention, the image pickupsystem of the 16th aspect is further characterized in that said viewingoptical system comprises two positive lens elements and one negativelens element.

No account is given of what is achieved by the 17th image pickup systembecause the same as referred to in conjunction with the 2nd image pickupsystem is achieved.

According to the eighteenth aspect of the invention, the image pickupsystem of the 16th aspect is further characterized in that said viewingoptical system has an aspheric lens surface.

No account is given of what is achieved by the 18th image pickup systembecause the same as referred to in conjunction with the 7th image pickupsystem is achieved.

According to the nineteenth aspect of the invention, the image pickupsystem of the 18th aspect is further characterized in that said lenselement having an aspheric surface is a plastic lens element.

No account is given of what is achieved by the 19th image pickup systembecause the same as referred to in conjunction with the 5th image pickupsystem is achieved.

According to the 20th aspect of the invention, the 16th image pickupsystem is further characterized in that said viewing optical systemconsists of two lens components or a doublet component composed of onenegative lens element and one positive lens element and one single-lenscomponent whose absolute value for refracting power is smaller thaneither one of the absolute value for refracting power of said positivelens element and the absolute value for refracting power of saidnegative lens element.

No account is given of what is achieved by the 20th image pickup systembecause the same as set forth in conjunction with the 8th image pickupsystem is achieved.

According to the 21st aspect of the invention, the 16th image pickupsystem is further characterized in that said viewing optical systemcomprises a single-lens component having an aspheric surface.

No account is given of what is achieved by the 21st image pickup systembecause the same as set forth in conjunction with the 9th image pickupsystem is achieved.

According to the 22nd aspect of the invention, the 16th image pickupsystem is further characterized in that said viewing optical systemconsists of three lens elements or, in order from said image displaydevice side, a positive lens element, a negative lens element and apositive lens element, while the first-mentioned positive lens elementis cemented together with said negative lens element.

No account is given of what is achieved by the 22nd image pickup systembecause the same as set forth in conjunction with the 11th image pickupsystem is achieved.

According to the 23rd aspect of the invention, the 16th image pickupsystem is further characterized in that said viewing optical systemconsists of three lenses or, in order from said image display deviceside, a positive lens element, a positive lens element and a negativelens element, while the first-mentioned positive lens element and saidnegative lens element are cemented together.

No account is given of what is achieved by the 23rd image pickup systembecause the same as set forth in conjunction with the 12th image pickupsystem is achieved.

According to the 24th aspect of the invention, there is provided animage pickup system comprising an image pickup device, an image displaydevice for displaying an image, a controller for converting imageformation obtained from said image pickup device into a signal thatenables said image information to be formed on said image displaydevice, and a viewing optical system for guiding an image displayed onsaid display device to a viewer's eye, characterized in that:

said viewing optical system consists of, in order from said image pickupdevice side, a negative single-lens component composed of one negativelens element and a positive single-lens component composed of onepositive lens element, and the following condition (1) is satisfied:0.6<b/a   (1)′Here the small letter a is a distance from the display screen of theimage pickup device to the surface, nearest to the image display deviceside, of the viewing optical system, and the small letter b is a totallength from the surface, axially nearest to the image display deviceside, of the viewing optical system to the surface thereof nearest tothe viewer side.

What is achieved by the 24th image pickup system is now explained.

To obtain a sufficient angle of field, the viewing optical system musthave a higher eyepiece magnification than a conventional one even whenan image pickup device of small size is used. To ensure a sufficientangle of field with two lenses even when an image pickup system of smallsize is used, therefore, the viewing optical system must be composed of,in order from the image pickup device, a negative single lens and apositive single lens. As a result, it is possible to spread out lightrays with the negative single lens and guide the light rays to aviewer's eyeball through the positive single lens, thereby securing thenecessary angle of field.

When the viewing optical system is constructed of two lenses, the lenssurface is spaced away from the image plane. This is preferable forpreventing an image being observed from becoming worse due to thedeposition of dust. For this reason, condition (1)′ is broader thancondition (1). As the lower limit of 0.6 to condition (1)′ is notreached or the whole length of the viewing optical system becomes short,it is required to increase the angle of refraction of axial and off-axislight rays through the viewing optical system, resulting in aberrationssuch as spherical aberrations, coma and chromatic aberration ofmagnification being likely to occur. Otherwise, the distance from thedisplay screen to the viewing optical system becomes too long to obtainthe necessary angle of field. As a matter of course, the lower limit tothis condition (1)′ may be set at 1.0 as in the case of condition (1).To reduce the whole size of the electronic view finder, it is preferableto meet the following condition (1-1):1.0<b/a<3.5   (1-1)

The same as mentioned above goes true for the lower limit of 1.0 to thiscondition (1-1). As the upper limit of 3.5 is exceeded, it is difficultto achieve compactness even when a more compact image display device isused, because the total length of the viewing optical system becomes toolong. Otherwise, the spacing between the display screen and the viewingoptical system becomes short; dust deposited on the viewing opticalsystem is more noticeable. In addition, it is difficult to take anoptical path for guiding illumination light when a reflection type imagedisplay device is used as the image display device.

More preferably, the following condition (1-2) should be satisfied:1.5<b/a<3.0   (1-2)

According to the 25th aspect of the invention, the 24th image pickupsystem is further characterized by satisfying the following condition(2):1.0<a/c   (2)Here the small letter a is the distance from the display screen of theimage pickup device to the surface, nearest to the image display deviceside, of the viewing optical system, and the small letter c is a lengthof the short side of the display screen of the image display device.

What is achieved by the 25th image pickup system is now referred to.

Condition (2) is provided to define the length from the display screento the viewing optical system with respect to the length of the shortside of the display screen. As the lower limit of 1.0 to condition (2)is not reached, dust deposited on the viewing optical system is morenoticeable. In addition, when a reflection type image display device isused, it is impossible to take any reflection optical path for guidingillumination light thereto.

To reduce the whole size of the electronic view finder, it is preferableto meet the following condition (2-1):1.0<a/c<4.5   (2-1)

The same as set forth above holds for the lower limit of 1.0 to thiscondition (2-1). As the upper limit of 4.5 is exceeded, any compactnessis never achievable even with a more compact image display device,because the spacing between the image display device and the viewingoptical system becomes too large.

More preferably, the following condition (2-2) should be satisfied:2.0<a/c<4.0   (2-2)

According to the 26th aspect of the invention, there is provided animage pickup system comprising an image pickup device, an image displaydevice for displaying an image, a controller for converting imageformation obtained from said image pickup device into a signal thatenables said image information to be formed on said image displaydevice, and a viewing optical system for guiding an image displayed onsaid display device to a viewer's eye, characterized in that:

said viewing optical system consists of, in order from said image pickupdevice side, a negative single-lens component composed of one negativelens element and a positive single-lens component composed of onepositive lens element,

said negative lens element is a double-concave lens element,

said positive lens element is a double-convex lens element,

of said negative lens element and said positive lens element, only saidpositive lens element has an aspheric surface,

a light beam from said image display device is guided by refractionalone to said viewer's eye, and the following condition (2) issatisfied:1.0<a/c   (2)Here the small letter a is a distance from the display screen of theimage pickup device to the surface, nearest to the image display deviceside, of the viewing optical system, and the small letter c is a lengthof the short side of the display screen of the image display device.

What is achieved by the 26th image pickup system is now explained.

To obtain a sufficient angle of field, the viewing optical system musthave a higher eyepiece magnification than a conventional viewing opticalsystem even when an image pickup device of small size is used. To ensurea sufficient angle of field with two lenses even when an image pickupsystem of small size is used, therefore, the viewing optical system mustbe composed of, in order from the image pickup device, a negative singlelens and a positive single lens. As a result, it is possible to spreadout light rays with the negative single lens and guide the light rays toa viewer's eyeball through the positive single lens, thereby securingthe necessary angle of field.

Condition (2) is provided to define the length from the display screento the viewing optical system with respect to the length of the shortside of the display screen. As the lower limit of 1.0 to condition (2)is not reached, dust deposited on the viewing optical system is morenoticeable. In addition, when a reflection type image display device isused, it is impossible to take any reflection optical path for guidingillumination light thereto.

To reduce the whole size of the electronic view finder, it is preferableto meet the following condition (2-1):1.0<a/c<4.5   (2-1)

The same as set forth above holds for the lower limit of 1.0 to thiscondition (2-1). As the upper limit of 4.5 is exceeded, any compactnessis never achievable even with a more compact image display device,because the spacing between the image display device and the viewingoptical system becomes too large.

More preferably, the following condition (2-2) should be satisfied:2.0<a/c<4.0   (2-2)

Especially for correction of aberrations, it is preferable to use adouble-concave lens for the negative single lens and a double-convexlens for the positive single lens, because the refracting power loadedon each lens can be allocated to both surfaces of each lens. Inaddition, as the light beam from the image display device is designed tobe guided by refraction alone to the viewer's eyeball, the image underobservation is lesser likely to become worse as compared with theprovision of a reflecting surface, because of no tilt due to thereflecting surface.

According to the 27th aspect of the invention, the 26th image pickupsystem is further characterized by satisfying the following condition(1):1.0<b/a   (1)Here the small letter a is a distance from the display screen of theimage pickup device to the surface, nearest to the image display deviceside, of the viewing optical system, and the small letter b is a totallength from the surface, axially nearest to the image display deviceside, of the viewing optical system to the surface nearest to the viewerside.

No account is given of what is achieved by the 27th image pickup systembecause the same as set forth in conjunction with the 13th image pickupsystem.

According to the 28th aspect of the invention, the 24th, 25th, 26th or27th image pickup system is further characterized by satisfying thefollowing condition (3):1.4<f _(e) /a<2.4   (3)Here the small letter a is the distance from the display screen of theimage pickup device to the surface, nearest to the image display deviceside, of the viewing optical system, and f_(e) is the focal length ofthe viewing optical system.

No account is given of what is achieved by the 28th image pickup systembecause the same as set forth in conjunction with the 15th image pickupsystem is achieved.

According to the 29th aspect of the invention, there is provided animage pickup system comprising an image pickup device, an image displaydevice for displaying an image, a controller for converting imageformation obtained from said image pickup device into a signal thatenables said image information to be formed on said image displaydevice, and a viewing optical system for guiding an image displayed onsaid display device to a viewer's eye, characterized in that:

said image display device has a display screen with a diagonal length inthe range of 2.5 mm to 8 mm.

What is achieved by the 29th image pickup system is now explained.

Preferably in this aspect, the image display device should have adisplay screen with a diagonal length in the range of 2.5 mm to 8 mm. Asthe lower limit of 2.5 mm is not reached, any angle of field necessaryfor observation is hardly obtained. As the upper limit of 8 mm isexceeded, the effect on reductions in the whole size of the electronicview finder becomes slender.

According to the 30th aspect of the invention, the 29th image pickupsystem is further characterized in that said viewing optical systemcomprises at least a lens element or at most three lens elements.

An account is given of what is achieved by the 30th image pickup system.

The incorporation of at least a lens element enables the viewing opticalsystem to work through at least two refracting surfaces. Theincorporation of at most three lens elements, on the other hand, keepsthe viewing optical system from being composed of lenses more thanrequired, resulting is some significant cost reductions. In addition,the incorporation of three lens elements in the viewing optical systemis preferable for correction of aberrations. To meet both requirementsfor cost and correction of aberrations, the viewing optical systemshould preferably be constructed of three lens elements.

According to the 31st aspect of the invention, the 29th image pickupsystem is further characterized in that the angle of field in a diagonaldirection of an image being observed through said viewing optical systemis in the range of 15° to 30°.

What is achieved by the 31st image pickup system is now explained.

The angle of field in the diagonal direction of the image being observedthrough the viewing optical system should be in the range of 15° to 30°.As the lower limit of 15° is not reached, it is difficult to observeimages in the image pickup range. As the upper limit of 30° is exceeded,the whole size of the electronic view finder can hardly be reduced.

More preferably, this angle of field should be in the range of 20° to26°.

According to the 32nd aspect of the invention, there is provided animage pickup system comprising an image pickup device, an image displaydevice for displaying an image, a controller for converting imageformation obtained from said image pickup device into a signal thatenables said image information to be formed on said image displaydevice, and a viewing optical system for guiding an image displayed onsaid display device to a viewer's eye, characterized in that:

said image display device is a reflection type image display device fordisplaying an image by illumination from a display screen side thereofand comprises an illumination member for illuminating the display screenof said reflection type image display device, and

said viewing optical system comprises a plurality of lens elements andfurther includes at least one aspheric surface.

What is achieved by the 32nd image pickup system is briefly explained.

For observing sharp images, it is more preferable to use a reflectiontype image display device as the image display device with the viewingoptical system comprising a plurality of lens elements and furtherincluding at least one aspheric surface, because it is possible to makeuse of the high aperture efficiency of that reflection type imagedisplay device.

According to the 33rd aspect of the invention, there is provided animage pickup system comprising an image pickup device, an image displaydevice for displaying an image, a controller for converting imageformation obtained from said image pickup device into a signal thatenables said image information to be formed on said image displaydevice, and a viewing optical system for guiding an image displayed onsaid display device to a viewer's eye, characterized in that:

said viewing optical system comprises a plurality of lens components inwhich all surfaces thereof, in contact with air, are convex on an airside, and an angle of field, 2Ω, in a diagonal direction of an imagebeing observed through said viewing optical system is at least 22.01°.

According to the 34th aspect of the invention, the 33rd image pickupsystem is further characterized in that the angle of field, 2Ω, in thediagonal direction of the image being observed through said viewingoptical system is at least 23.01°.

What is achieved by the 33rd and 34th image pickup systems is nowdescribed.

For the viewing optical system it is required to have positiverefracting power. Preferably in this case, however, the positiverefracting power should be dispersed. By using a plurality of lenscomponents in which all the surfaces thereof, in contact with air, havepositive powers, it is thus easy to make the angle of field wide. If theangle of field, 2Ω, in the diagonal direction of the image underobservation is at least 22.01°, it is then easy to see the image large.In particular, the angle of field of 22.01° makes observation easier.

According to the 35th aspect of the invention, the 1st, 16th, 24th,26th, 32nd or 33rd image pickup system is further characterized in thata diagonal length of the display screen of said image display device isin the range of 2.5 mm to 8 mm.

No account is given of what is achieved by the 35th image pickup systembecause the same as set forth in conjunction with the 29th image pickupsystem is achieved.

According to the 36th aspect of the invention, the 1st, 16th, 24th or26th image pickup system is further characterized in that the angle offield in the diagonal length of the image being observed through saidviewing optical system is in the range of 15° to 30°.

No account is given of what is achieved by the 36th image pickup systembecause the same as mentioned in conjunction with the 31st image pickupsystem is achieved.

According to the 37th aspect of the invention, the 1st, 16th, 24th,26th, 29th or 33rd image pickup system is further characterized in thatsaid image display device is a reflection type image display device fordisplaying an image by illumination from a display screen side thereof,and comprises an illumination member for illuminating the display screenof said reflection type image display device.

No account is given of what is achieved by the 37th image pickup systembecause the same as mentioned in conjunction with the 32nd image pickupsystem is achieved.

According to the 38th aspect of the invention, the 16th, 29th or 32ndimage pickup system is further characterized in that said viewingoptical system comprises a plurality of lens components in which allsurfaces thereof, in contact with air, are convex on an air side.

No account is given of what is achieved by the 38th image pickup systembecause the same as mentioned in conjunction with the 33rd image pickupsystem is achieved.

According to the 39th aspect of the invention, the 1st, 16th, 24th,26th, 29th, 32nd or 33rd image pickup system is further characterized byfurther comprising a phototaking optical system for guiding a light beamto said image pickup device.

What is achieved by the 39th image pickup system is now explained.

While the present invention has been described on the premise that thephototaking optical system is used, it is understood that the imagepickup system proper may be provided with a mount at which replaceablephototaking optical systems are arbitrarily mounted. Such an imagepickup system free from any phototaking optical system, too, is includedin the image pickup system of the invention.

It is also understood that if an image pickup optical system for guidinga light beam to the image pickup device is used as in the 39th imagepickup system, it is then possible to observe a subject's imagedepending on the properties (angle of view, depth of focus, etc.) of theimage pickup optical system.

According to the 40th aspect of the invention, there is provided animage pickup system comprising an image pickup device, an image displaydevice for displaying an image, a controller for converting imageformation obtained from said image pickup device into a signal thatenables said image information to be formed on said image displaydevice, and a viewing optical system for guiding an image displayed onsaid display device to a viewer's eye, characterized in that:

said viewing optical system consists of two single-lens elements or, inorder from said display device side, a single-lens element in a negativemeniscus form convex on said display device side and a positivesingle-lens element in a double-convex form, and surfaces located from adisplay screen to a viewer's eyeball are all composed only of refractingsurfaces.

What is achieved by the 40th image pickup system is now explained.

With the lens arrangement where the negative single-lens element and thedouble-convex positive single-lens element are located in order from thedisplay screen side, it is possible to secure a wide field.

Preferably in this case, the negative lens element should be in ameniscus form convex on the display screen side, because the surface ofpositive power, the surface of negative power and the surface ofpositive power are arranged in order from the display screen side sothat aberrations can be well corrected with a reduced number of lenses.

Furthermore, much more simplified construction is achievable because ofno reflection of an optical path from the display screen.

According to the 41st aspect of the invention, the 40th image pickupsystem is further characterized by satisfying the following condition(3):1.4<f _(e) /a<2.4   (3)Here the small letter a is the distance from the display screen of theimage pickup device to the surface, nearest to the image display deviceside, of the viewing optical system, and f_(e) is the focal length ofthe viewing optical system.

No account is given of what is achieved by the 41st image pickup systembecause the same as mentioned in conjunction with the 15th image pickupsystem is achieved.

According to the present invention, a plurality of the aforesaid aspectsmay be used in suitable combinations while the effect of each aspect iskept intact.

Even though only the upper or lower limit to each condition issatisfied, the effect corresponding to that limit may be achievable.

It is also understood that the values referred to in the followingexamples may be used as the upper or lower limit values.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction,combinations of elements, and arrangement of parts which will beexemplified in the construction hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is illustrative in schematic of the construction of a digitalcamera that is one embodiment of the image pickup system according tothe invention.

FIG. 2 is illustrative of the construction of a sliver-salt camera towhich the image pickup system of the invention is applied.

FIG. 3 is illustrative of the construction of a typical electronic viewfinder according to the invention.

FIGS. 4(a) through 4(d) are sectional views inclusive of the opticalaxes of the viewing optical systems in Examples 1 to 4 of the invention.

FIGS. 5(a) through 5(c) ae sectional views inclusive of the optical axesof the viewing optical systems in Examples 5 to 7 of the invention.

FIG. 6 is an aberration diagram for the viewing optical system ofExample 1.

FIG. 7 is an aberration diagram for the viewing optical system ofExample 2.

FIG. 8 is an aberration diagram for the viewing optical system ofExample 3.

FIG. 9 is an aberration diagram for the viewing optical system ofExample 4.

FIG. 10 is an aberration diagram for the viewing optical system ofExample 5.

FIG. 11 is an aberration diagram for the viewing optical system ofExample 6.

FIG. 12 is an aberration diagram for the viewing optical system ofExample 7.

DESCRIPTION OF THE PREFERRED EMBODIMENS

Some embodiments of the image pickup system according to the inventionare now explained.

FIG. 1 is illustrative of the construction of a digital camera that isone embodiment of the image pickup system according to the invention.

Referring to FIG. 1, reference numeral 10 indicates an image pickupsystem or a digital camera comprising an image pickup optical system 1,a filter 2, an image pickup device 3, a controller 4, a built-in memory5, an electronic view finder 6, and an interface 7.

In the aforesaid image pickup system, light emanating from an objectpoint is focused through the image pickup system 1 comprising opticalelements (such as lenses) on the light-sensing surface of the imagepickup device 3 such as a CCD to form an object image thereon. The imagepickup device 3 is an array of regularly arranged photoelectricconverters, and between the image pickup system 1 and the image pickupdevice 3 there is located a filter 2 having a low-pass effect onprevention of a moire phenomenon due to such an array. In some cases, aninfrared cut filter for cutting off infrared light may be located.

A light beam incident on the image pickup device 3 is converted by thephotoelectric converters to electric signals which are then inputtedinto the controller 4, where they are subjected to image processing suchas gamma correction and image compression and then sent to a personalcomputer 9 or the like via the built-in memory 5 and interface 7.

The resultant signals are then transmitted to a reflection type imagedisplay device (not shown in FIG. 1), from which they are fed to theelectronic view finder 6 comprising an illumination system, a reflectiontype image display device, a viewing optical system or the like, so thatthe image to be picked up or the picked up image can be observed by anobserver. Image data may be sent from the built-in memory 5 to anauxiliary memory 8, while the same image data may be sent from theinterface 7 to the personal computer 9.

FIG. 2 is illustrative of the construction of a silver-salt camera towhich the image pickup system according to the invention is applied. Asshown in FIG. 2, a silver-salt camera 20 comprising the image pickupsystem of the invention is provided with an image pickup optical system11, a film 12, an objective lens 13, an image pickup device 14 such as aCCD, a first controller 15 and another or a second controller 16 as wellas, as in the case of the FIG. 1 digital camera, a built-in memory 5 andan electronic view finder 6.

In the silver-salt camera 20 shown in FIG. 2, a light beam from anobject point is focused through the image pickup optical system 11 onthe film 12 to form an object image thereon. A light beam from theobject point is also focused through the objective lens 13 separate fromthe image pickup optical system 11 on the image pickup device 14 such asa CCD to form an object image thereon. The light beam incident on theimage pickup device 14 is converted by photoelectric converters formingthe image pickup device 14 to electric signals, which are then inputtedinto the first controller 15, where they are subjected to imageprocessing such as gamma correction and image compression and then sentto a reflection type image display device and fed to the electronic viewfinder 6 constructed of an illumination system, a reflection type imagedisplay device, a viewing optical system, etc., so that the image to bepicked up can be observed by an observer.

On the other hand, if information, etc. stored by the controller 15 inthe built-in memory 5 are used, it is then possible for the user(observer) to view the picked-up image.

The second controller 16 is provided to control the image pickup opticalsystem 11. On the basis of signals from the second controller 16, thefirst controller 15 may recognize information on the zooming, focusing,etc. of the image pickup optical system 11, so that adjustments are madedepending on the image pickup angle of view of the image to be displayedon the reflection type image display device. Alternatively, the secondcontroller 16 may recognize information on the focusing, etc. of theimage pickup optical system 11, so that the range of the image displayedon the reflection type display device is corrected (for parallax). Stillalternatively, signals may be sent from the first controller 15 to thebuilt-in memory 5 or an interface (not shown), thereby producing outputon a personal computer or the like.

Further, the objective lens 13 may be dispensed with. For instance, alight beam from the image pickup optical system 11 may be split into twoor more beams, one of which is used for finder purposes. This finderlight beam is used to form an image on the image pickup device 14 suchas a CCD for viewing purposes.

Next, the electronic view finder used herein is explained.

FIG. 3 is illustrative of the construction of a typical electronic viewfinder used herein. Reference numerals 21R, 21G and 21B represent a redlight source, a green light source and a blue light source,respectively. For instance, light-emitting diodes are used. Referencenumeral 22 stands for an illumination optical system, 23 a viewingoptical system, 24 the optical axis of the viewing optical system 23, 25a viewer's eye,.26 a reflection type image display device, and 27 aplane-parallel plate with a polarizing half-silvered mirror 28 mountedthereon.

In the thus constructed finder, illumination light from the lightsources 21R, 21G and 21B is reflected by the illumination optical system22 comprising a reflecting mirror in one direction (upwardly in FIG. 3).The optical axis 24 of the viewing optical system 23 is designed tointersect vertically the substantial center of the image display device26.

Leaving the light sources 21R, 21G and 21B and reflected by theillumination optical system 22 constructed of a reflecting mirror in onedirection, illumination light propagates with its center intersectingalmost vertically the optical axis 24 of the viewing optical system 23,and is then reflected at the half-silvered mirror 28 toward thereflection type image display device 26.

The reflection type image display device 26 used is a reflection typetwisted nematic liquid crystal display device with its twist angle setat 45°.

An image displayed on this reflection type display device 26 is viewedby an observer via the viewing optical system 23 through theplane-parallel plate 27 with the polarizing half-silvered mirror 28mounted thereon.

In the electronic view finder of such construction, when theillumination light emanating from the light sources 21R, 21B and 21B isin a randomly polarized state, it is linearly polarized by thepolarizing half-silvered mirror 28 in a certain direction forilluminating the liquid crystal display device 26. For instance, whenthe polarizing half-silvered mirror 28 is designed in such a way as toreflect S waves and transmit P waves, the illumination light reflectedat the half-silvered mirror 28 is defined by S waves. Reflected at thehalf-silvered mirror 28 to illuminate the liquid crystal display device26 that is an image display device, the illumination light passesthrough voltage-applied pixels and a liquid crystal layer, at the bottomof which it is reflected, leaving with the polarizing direction turnedthrough 90°. Thus, the illumination light, which has been entered as Swaves into the image pickup display device 26 and modulated thereat,leaves in the form of P waves. Upon re-incidence on the plane plate 27,nearly all this P-wave light transmits through the polarizinghalf-silvered mirror 28, arriving at a viewer's eye 25 via the viewingoptical system 23.

The light sources 21R, 21G and 21B are put on in order, so that red,green and blue light rays are successively guided to the liquid crystaldisplay device 26. In turn, the liquid crystal display device 26displays successively images corresponding to the thus guided lightrays, so that color images are formed.

As mentioned above, the electronic view finder used herein can be acompact, light-weight finder that is simplified in construction, andmakes effective use of light, because of no substantial losses in thequantity of light emanating from the light sources 21R, 21G and 21B. Theaction of the viewing optical system 23 enables the observer to perceiveimages on the image display device 26 as virtual images on an enlargedscale. Preferably in this case, the electronic view finder should bedesigned such that an illumination optical path where light beamsleaving the light sources 21R, 21G and 21B enter the image displaydevice 26 upon reflection at the polarizing half-silvered mirror 28 anda viewing optical path where light beams reflected at the image displaydevice 26 are guided to the viewer's eye upon transmission through thepolarizing half-silvered mirror 28 form a reciprocating optical pathbetween the polarizing half-silvered mirror 28 and the image displaydevice 26. With this arrangement, the optical path through the viewingoptical system can be used as a combined forward and backward opticalpath, so that wasted optical elements (transmitting surfaces orreflecting surfaces) and space can be eliminated unlike an opticalsystem having separate two optical paths, thereby making the imagepickup system compact. This arrangement is also helpful for preventionof flare light.

In the finder shown in FIG. 3, it is noted that a curved surface such asa rotationally symmetric paraboloid may be used instead of thehalf-silvered mirror 28. It is also noted that the illumination opticalsystem 22 may be located at an optical path passing through thehalf-silvered mirror 28 and the viewing optical system 23 may bepositioned at an optical path for reflecting the half-silvered mirror26. In the case, the distance a from the display screen of the imagedisplay device 26 to the surface of the viewing optical system 23located nearest to the image display device 26 side is understood tomean the length of that optical path.

The viewing optical system 23 in the electronic view finder shown inFIG. 3 may be constructed as in the following examples.

In the following Examples 1 to 5, the display screen is in a rectangularform having a length of 3.84 mm in the horizontal direction and a lengthof 2.88 mm in the vertical (short-side) direction with a diagonal lengthof 4.8 mm. In the following Example 6, the display screen is in arectangular form having a length of 8.96 mm in the horizontal directionand a length of 6.66 mm in the vertical (short-side) direction with adiagonal length of 11.164 mm.

FIGS. 4(a) through 4(d) are sectional views including the optical axesof the viewing optical systems according to Examples 1 to 4, and FIGS.5(a) through 5(c) are sectional views including the optical axes of theviewing optical systems according to Examples 5 to 7. Numerical data onthese examples will be enumerated later. In each example, “LCD”represents a liquid crystal display device forming part of the imagedisplay device, “EP” an eye point”, and “L” the diagonal length of theimage display device.

As shown in FIG. 4(a), the viewing optical system of Example 1 iscomposed of, in order from the image display device side, adouble-convex positive lens and a doublet consisting of a double-convexpositive lens and a negative meniscus lens concave on its object side,while the surface nearest to the eye point side is formed of an asphericsurface.

The values for conditions (1) to (3) in this example and the angle offield, 2Ω, in the diagonal direction of an image under observation areas follows:

-   -   a=6.59 mm    -   b=16.06 mm    -   c=2.88 mm    -   f_(e)=12.77 mm    -   b/a=2.435    -   a/c=2.289    -   f_(e)/a=1.937    -   2Ω=22.01°

As shown in FIG. 4(b), the viewing optical system of Example 2 iscomposed of, in order from the display device side, a doublet consistingof a double-convex positive lens and a negative meniscus lens concave onits object side and a double-convex positive lens, while the objectside-surface of the double-convex positive lens located on an eye pointside is formed of an aspheric surface.

The values for conditions (1) to (3) in this example and the angle offield, 2Ω, in the diagonal direction of an image under observation areas follows:

-   -   a=7.00 mm    -   b=13.12 mm    -   c=2.88 mm    -   f_(e)=11. 97 mm    -   b/a=1.876    -   a/c=2.430    -   f_(e)/a=1.710    -   2Ω=23.01°

As shown in FIG. 4(c), the viewing optical system of Example 3 iscomposed of, in order from a display device side, a double-convexpositive lens and a doublet consisting of a double-convex positive lensand a negative meniscus lens concave on its object side, while thesurface, on an eye point side, of the double-convex positive lens on theobject side is formed of an aspheric surface.

The values for conditions (1) to (3) in this example and the angle offield, 2Ω, in the diagonal direction of an image under observation areas follows:

-   -   a=6.52 mm    -   b=15.13 mm    -   c=2.88 mm    -   f_(e)=12.09 mm    -   b/a=2.319    -   a/c=2.265    -   f_(e)/a=1.853    -   2Ω=23.03°

As shown in FIG. 4(d), the viewing optical system of Example 4 iscomposed of, in order from a display device side, a negative meniscuslens convex o its object side and a double-convex positive lens whilethe object-side surface of the double-convex positive lens is formed ofan aspheric surface.

The values for conditions (1) to (3) in this example and the angle offield, 2Ω, in the diagonal direction of an image under observation areas follows:

-   -   a=12.28 mm    -   b=8.03 mm    -   c=2.88 mm    -   f_(e)=18.24 mm    -   b/a=0.654    -   a/c=4.266    -   f_(e)/a=1.485    -   2Ω=15.05°

As shown in FIG. 5(a), the viewing optical system of Example 5 iscomposed of, in order from a display device side, a double-concavenegative lens and a double-convex positive lens, while the eyepoint-side surface of the double-convex positive lens is formed of anaspheric surface.

The values for conditions (1) to (3) in this example and the angle offield, 2Ω, in the diagonal direction of an image under observation areas follows:

-   -   a=10.91 mm    -   b=8.49 mm    -   c=2.88 mm    -   f_(e)=18.24 mm    -   b/a=0.778    -   a/c=3.789    -   f_(e)/a=1.671    -   2Ω=15.45°

As shown in FIG. 5(b), the viewing optical system of Example 6 is madeup of, in order from a display device side, a double-concave negativelens and a double-convex positive lens while the object-side surface ofthe double-convex positive lens is formed of an aspheric surface.

The values for conditions (1) to (3) in this example and the angle offield, 2Ω, in the diagonal direction of an image under observation areas follows:

-   -   a=14.64 mm    -   b=9.16 mm    -   c=6.66 mm    -   f_(e)=21.21 mm    -   b/a=0.626    -   a/c=2.198    -   f_(e)/a=1.448    -   2Ω=30.04°

As shown in FIG. 5(c), the viewing optical system of Example 7 is madeup of, in order from a display device side, a negative meniscus lensconvex on the display device side and a double-convex positive lenswhile the object-side surface of the double-convex positive lens isformed of an aspheric surface. In this example, there is used atransmission type liquid crystal display device wherein light sourcesare located on the back side of a display screen so that an image isformed by light transmitting through the transmission type liquidcrystal display device.

The values for conditions (1) to (3) in this example and the angle offield, 2Ω, in the diagonal direction of an image under observation areas follows:

-   -   a=15.04 mm    -   b=10.38 mm    -   c=6.66 mm    -   f_(e)=21.27 mm    -   b/a=0.69    -   a/c=2.26    -   f_(e)/a=1.41    -   2Ω=30.02°

In what follows, numerical data on each example will be given. It isnoted that r₁, r₂, . . . represent the radius of curvature of each lenssurface, d₁, d₂, . . . represent the spacing between lens surfaces,n_(d1), n_(d2), . . . represent the d-line refractive index of eachlens, and ν_(d1), ν_(d2), . . . represent the Abbe number of each lens.It is also noted that ro stands for the radius of curvature of thedisplay screen of “LCD”, d₀ indicates the spacing between the displayscreen of “LCD” and the first lens surface, r₆ in Examples 1-3 and r₅ inExamples 4-6 each show the radius of curvature of the “EP” surface, andd₅ in Examples 1-3 and d₄ in Examples 4-6 each represent an eye relief.Length is given in mm. Here let x stand for an optical path providedthat the direction of propagation of light is positive and y indicate adirection perpendicular to the optical axis. Aspheric surface shape isgiven byx=(y ² /r)/[1+{1−(K+1)(y/r)²}^(1/2) ]+A ₄ y ⁴ +A ₆ y ⁶ +A ₈ y ⁸Here r is a paraxial radius of curvature, K is a conical coefficient,and A₄, A₆ and A₈ are the 4th, 6th and 8th aspheric coefficients,respectively.

EXAMPLE 1

r₀ = ∞ (LCD) d₀ = 6.59 r₁ = 52.055 d₁ = 6.86 n_(d1) = 1.58913 ν_(d1) =61.14 r₂ = −11.570 d₂ = 1.09 r₃ = 54.042 d₃ = 6.06 n_(d2) = 1.56384ν_(d2) = 60.67 r₄ = −9.258 d₄ = 2.05 n_(d3) = 1.80518 ν_(d3) = 25.42 r₅= −17.680 (Aspheric) d₅ = 17.00 r₆ = ∞ (EP)Aspherical Coefficients

5 th SurfaceK=0.000A ₄=1.57513×10⁻⁵A ₆=2.15451×10⁻⁷A ₈=−4.32763×10⁻⁹

EXAMPLE 2

r₀ = ∞ (LCD) d₀ = 7.00 r₁ = 10.449 d₁ = 7.54 n_(d1) = 1.56384 ν_(d1) =60.67 r₂ = −14.467 d₂ = 1.64 n_(d2) = 1.80518 ν_(d2) = 25.42 r₃ =−114.013 d₃ = 0.50 r₄ = 20.456 (Aspheric) d₄ = 3.45 n_(d3) = 1.58913ν_(d3) = 61.14 r₅ = −18.079 d₅ = 17.00 r₆ = ∞ (EP)Aspherical Coefficients

4 th SurfaceK=0.000A ₄=−3.29162×10⁻⁴A ₆=1.70351×10⁻⁶A ₈=−7.06260×10⁻⁸

EXAMPLE 3

r₀ = ∞ (LCD) d₀ = 6.52 r₁ = 52.055 d₁ = 8.25 n_(d1) = 1.58913 ν_(d1) =61.14 r₂ = −10.708 (Aspheric) d₂ = 0.30 r₃ = 34.600 d₃ = 5.78 n_(d2) =1.56384 ν_(d2) = 60.67 r₄ = −9.258 d₄ = 0.80 n_(d3) = 1.80518 ν_(d3) =25.42 r₅ = −23.115 d₅ = 17.00 r₆ = ∞ (EP)Aspherical Coefficients

2nd SurfaceK=0.000A ₄=4.79644×10⁻⁵A ₆=−6.80364×10⁻⁷A ₈=5.86617×10⁻⁹

EXAMPLE 4

r₀ = ∞ (LCD) d₀ = 12.28 r₁ = 50.414 d₁ = 1.06 n_(d1) = 1.58423 ν_(d1) =30.49 r₂ = 9.124 d₂ = 0.55 r₃ = 9.908 (Aspheric) d₃ = 6.42 n_(d2) =1.49236 ν_(d2) = 57.86 r₄ = −9.014 d₄ = 17.00 r₅ = ∞ (EP)Aspherical Coefficients

3 rd SurfaceK=0.000A ₄=−4.23266×10⁻⁴A ₆=1.26605×10⁻⁵A ₈=−1.87739×10⁻⁷

EXAMPLE 5

r₀ = ∞ (LCD) d₀ = 10.91 r₁ = −26.234 d₁ = 1.06 n_(d1) = 1.58423 ν_(d1) =30.49 r₂ = 24.828 d₂ = 1.51 r₃ = 13.612 d₃ = 5.92 n_(d2) = 1.49236ν_(d2) = 57.86 r₄ = −8.868 (Aspheric) d₄ = 17.00 r₅ = ∞ (EP)Aspherical Coefficients

4 th SurfaceK=0.000A ₄=2.46412×10⁻⁴A ₆=2.50349×10⁻⁶A ₈=1.52473×10⁻⁸

EXAMPLE 6

r₀ = ∞ (LCD) d₀ = 14.64 r₁ = −37.022 d₁ = 1.02 n_(d1) = 1.58423 ν_(d1) =30.49 r₂ = 52.882 d₂ = 1.32 r₃ = 15.833 (Aspheric) d₃ = 6.82 n_(d2) =1.52542 ν_(d2) = 55.78 r₄ = −13.482 d₄ = 17.00 r₅ = ∞ (EP)Aspherical Coefficients

3rd SurfaceK=0.000A ₄=−2.24211×10⁻⁴A ₆=6.92370×10⁻⁷A ₈=−1.96757×10⁻⁹

EXAMPLE 7

r₀ = ∞ (LCD) d₀ = 15.04 r₁ = 68.309 d₁ = 1.77 n_(d1) = 1.58423 ν_(d1) =30.49 r₂ = 17.414 d₂ = 0.71 r₃ = 13.379 (Aspheric) d₃ = 7.90 n_(d2) =1.52542 ν_(d2) = 55.78 r₄ = −15.234 d₄ = 17.00 r₅ = ∞ (EP)Aspherical Coefficients

3 rd SurfaceK=0.000A ₄=−1. 72329×10⁻⁴A ₆=7.59604×10×⁻⁷A ₈=−5. 05665×10⁻⁹

FIGS. 6 to 12 are aberration diagrams for Examples 1 to 7, in which“SA”, “AS” and “CC” represent spherical aberrations, astigmatism andchromatic aberration of magnification, respectively.

As can be appreciated from the foregoing, the present invention canprovide such image pickup systems as summarized below:

an image pickup system having an electronic view finder suitable forachieving compactness;

an image pickup system that enables an observer to have an easy grasp ofthe image pickup range;

an image pickup system that gets hold of a sufficient angle of field andsatisfactory optical performance even when using an image display deviceprovided with a display screen having a short diagonal length;

an image pickup system having an electronic view finder withwell-corrected chromatic aberration of magnification;

an image pickup system provided with an electronic view finder whereindust, etc. deposited on a viewing optical system are unnoticeable; and

an image pickup system provided with an electronic view finder thatenables appropriate optical elements to be located even when areflection type image display device is used as an image display device.

1. An image pickup system comprising an image pickup device, an imagedisplay device for displaying an image, a controller for convertingimage formation obtained from said image pickup device into a signalthat enables said image information to be formed on said image displaydevice, and a viewing optical system for guiding an image displayed onsaid display device to a viewer's eye, wherein: said image displaydevice is a reflection type image display device for displaying an imageby illumination from a display screen side thereof and comprises anillumination member for illuminating a display screen of said reflectiontype image display device, and said viewing optical system comprises aplurality of lens elements and further includes at least one asphericsurface.
 2. The image pick-up system according to claim 1 wherein: saidobservation system comprises a plurality of lens components in whichlens surfaces in contact with air all have a convex surface directedtoward an air side, and an angle of field, 2Ω, in a diagonal directionof an observation image observed by said observation optical system isat least 22.01°.
 3. The image pickup system according to claim 2,wherein: the field angle of 2Ω in a diagonal direction of an observationimage observed by said observation optical system is at least 23.01°. 4.The image pickup system according to claim 1 wherein a diagonal lengthof the display screen of said image display device is in the range of2.5 mm to 8 mm.
 5. The image pickup system according to claim 1 whereinthe angle of field in the diagonal length of the image being observedthrough said viewing optical system is in the range of 15° to 30°. 6.The image pick-up system according to claim 1 wherein: said viewingoptical system comprises a plurality of lens components in which allsurfaces thereof, in contact with air, are convex on an air side, saidviewing optical system comprises at least three lens elements, andwherein the following conditions (1) and (3) are satisfied:1.0<b/a   (1)1.4<f _(e) /a<2.4   (3) where a is a distance from the display screen ofsaid image display device to the surface, nearest to the image displaydevice side, of said viewing optical system, b is a total length fromthe surface, axially nearest to the image display device side, of saidviewing optical system to the surface thereof nearest to the viewerside, and f_(e) is a focal length of said viewing optical system.
 7. Theimage pickup system according to claim 1 which further comprises aphototaking optical system for guiding a light beam to said image pickupdevice.
 8. The image pick-up system according to claim 1 wherein: saidviewing optical system consists of, in order from a display device side,a single-lens element having a negative meniscus shape with a convexsurface directed toward the display device side and a positivesingle-lens element having a double-convex shape.